1. Field of the Invention
The present invention relates to a bonding method for a rotor of an electric rotating machine, a welding apparatus for the rotor of the electric rotating machine and the rotor of the electric rotating machine.
2. Description of Related Art
"A Method For Bonding An Armature Coil" has been proposed by Japanese Patent Application No. Hei 8-15088 and is shown in FIGS. 12A, 12B, 13A, 13B, 14A and 14B.
The armature disclosed in this application has a lower layer coil 4 and an upper layer coil 5 which are assembled to an armature core 3 as illustrated in FIGS. 12A and 12B. The coils 4 and 5 are composed of a lower layer coil side 4a and upper layer coil side 5a, respectively disposed in slots 3a of the armature core 3. The coils 4 and 5 also include a lower layer coil end portion 4b and upper layer coil end portion 5b extending from the axial ends of both coil sides 4a, 5a to the inner-peripheral side substantially in parallel with the axial end face of the armature core 3. The coils 4 and 5 further include and a lower layer coil protrusion portion 4c and upper layer coil protrusion portion 5c axially protruding from inner-peripheral radial ends of both coil end portions 4b, 5b. Both coil protrusion portions 4c, 5c are radially superposed one over the other at an outer periphery of the rotating shaft and are welded to each other by TIG (tungsten inert gas) welding with a welding torch (not illustrated) being directed to a prescribed position (e.g., a substantially central portion of the bond-boundary portion) of forward ends of the both coil protrusion portions 4c, 5c.
However, when both coil protrusion portions 4c, 5c are bonded together by the above bonding technique with the welding torch being directed to one point which is the prescribed position of the forward ends thereof, the spherical bonded portions 25 such as those illustrated in FIGS. 13A and 13B are produced at several of a plurality of the bonded portions (each composed of both coil protrusion portions 4c, 5c).
As illustrated in FIG. 14B, this spherical bonded portion 25 is in a state where circumferential bulgings 25d of the fused base metal become large with the result that a circumferential width 25 W is appreciably greater than a circumferential width 5 W of the coil protrusion portions 4c, 5c before mutual bond therebetween. For this reason, to which there is added the reason why, as illustrated in FIG. 12B, a plurality of the bonded portions (each composed of both coil protrusion portions 4c, 5c) are provided circumferentially closely to each other, there is a high likelihood that the bonded portion 25 of both coil protrusion portions 4c, 5c may abut against another circumferentially adjacent bonded portion 25 of both coil protrusion portions 4c, 5c and be short-circuited thereto.
Also, as illustrated in FIG. 14A, the fusion depth L of the bonded portion 25 becomes inconveniently small with the result that the fusion-sectional area of the bonded portion 25 becomes inconveniently small and as a result the electric resistance becomes high.